Issue with connecting to WiFi

Hello, I often have problems connecting to WiFi networks. The error I get is:

"Unable to join the network "SSID NAME"
This network operates on Wi-Fi channels that are also used by several nearby networks.
Restarting the wireless router may allow it to automatically select the best channel and thus resolve the issue.

When it comes to configuring the Access Points themselves, networks 2.4 and 5 are enabled, channels on 2.4 are 1,6,11. No interference. What could be the reason for such a message? The device on which the problem was noticed is an iPhone 16 Pro.

Hardware:
- AP - FAP-231G
- UTM - FG40F

- Switch - FortiSwitch

Update: I have native NAC applied in my network.